The biogenesis of cell surface membrane will be studied during ciliary regeneration in the microbial eucaryote, Tetrahymena. When these cells are completely deciliated, approximately one half of the total surface membrane is removed. This relatively large quantity of surface membrane is replaced within 3 hours as the cilia regenerate, and the entire process can occur in non-nutrient medium. In this system, it will be possible to explore the interrelations which exist between the synthesis of membrane proteins, phospholipids, and carbohydrates, and to determine the relative contributions of induced synthesis and preformed reservoirs to ciliary membrane formation. The recent hypothesis that surface membranes may be formed from pre-existing membrane stores within the cell will be tested directly in our studies of induced synthesis of membrane components during membrane regeneration in Tetrahymena. Evidence for reservoirs will also be sought using ultrastructural methods. In addition to conventional electron microscopy, surface probes which can be visualized by electron microscopy will be attached to the cell surface, then the migration of these will be followed during ciliary regeneration. Membrane regression can also be induced and controlled in Tetrahymena. Studies of the synthesis and migration of membrane of membrane components during regeneration coupled to regression are expected to greatly facilitate the investigation of control mechanisms. The hypothesis that membrane modulation may be accomplished by selective exocytosis will be tested, and the existence of spatial controls over the cell surface will be explored by comparing oral and somatic ciliary membrane biogenesis.